The invention relates to a drug delivery device comprising a housing with a drug container, said drug container having delivering means comprising a piston for expelling a drug from the drug container, said housing further comprising a displaceable piston rod abutting the piston of the drug container, rotating means being in engagement with the piston rod, said rotating means being provided with a one-way mechanism.
The delivery device may be of any type that delivers a liquefied drug to a person as an aerosol spray, an injection or a high-pressure jet. Preferably, however, the delivery device is an injection syringe that may be of a single-use type or a type having an exchangeable drug container or cartridge.
A drug delivery device of this kind is known from U.S. Pat. No. 4,367,739 that discloses a syringe provided with a threaded actuating rod with a piston that is arranged in a container or barrel containing the drug. The actuating rod is provided with a knurled knob at the end opposite the piston, said knurled knob being provided with a one-way mechanism. The one-way mechanism comprises a ratchet lock that may be released by manually disengaging a ratchet tooth from a ratchet wheel.
This type of one-way mechanisms is known in a number of appliances where movement in one direction is allowed while movement in an opposite direction is prevented. The movement may be linear or rotating.
Although widely used, manufacturing of a ratchet lock is relatively complicated since it comprises manufacturing of a ratchet tooth part and a ratchet wheel, each having matching teeth, and mounting each of these parts with cooperating parts of the device in which the ratchet lock is to be used. Finally, the cooperating parts are assembled.
It is an object of the present invention to provide a drug delivery device with a rotatable axle provided with a one-way mechanism that is structurally simpler than the previously known one-way mechanisms of the known devices.
This is achieved by providing the drug delivery device mentioned in the opening paragraph with a one-way mechanism that comprises a helical spring wound tightly around said axle, one end of said helical spring being fixed in relation to the housing, the other end of the helical spring being in a free state.
By arranging the one-way mechanism in this way a very simple and yet reliable one-way mechanism is provided. Further, the one-way mechanism is easy to build into a drug delivery device since it comprises very few parts.
The drug delivery device may be of a single-use type or a type having an exchangeable drug container or cartridge. If the drug delivery device is of the latter type, a release button is provided, said release button being able to displace the free end of the helical spring in a direction of unwinding the helical spring. Thereby the helical spring loses its frictional engagement with the axle and the axle is free to rotate in either direction.
In this way the piston rod can be retracted from the cartridge and the cartridge can be exchanged.
In a preferred embodiment the piston rod is provided with a toothing and is in engagement with a piston rod driving wheel provided with a complementary toothing, said piston rod driving wheel being mounted on said axle. In this embodiment, displacement of the piston rod is provided by rotating the axle, said rotation being provided by any known means, e.g. by a push button in engagement with the axle or by an electric motor.
In order to minimize the size of the drug delivery device the piston rod may be flexible and is positioned partly around the piston rod driving wheel. A guiding face may be provided in the housing, said flexible piston rod being positioned between said guiding face and said piston rod driving wheel.